The present invention relates generally to dry semiconductor processing, and specifically to a method of residual resist removal after etching of aluminum or aluminum alloy films in chlorine containing plasma.
Integrated circuit (IC) technology has advanced from large scale integration (LSI), to very large scale integration (VLSI), and to ultra-large scale integration (ULSI) due to the development of four basic cornerstones. Those four cornerstones are: (1) photo-masking processes; (2) layer formation processes; (3) doping processes; and (4) etching processes.
These four factors made it possible to incorporate into IC chips a lot on increasingly complex devices and circuits. On the other hand, they allowed the use of greater device densities and smaller minimum feature sizes and smaller isolation.
Nowadays, dry etching of metal films is the only available method because it can provide anisotropic etching of submicron features. For plasma etching of aluminum or aluminum alloy films, chlorine containing compounds are used because AlCl3 is the most volatile compound among any other aluminum containing compounds.
However, there is one significant disadvantage of chlorine containing plasma etching of aluminum/aluminum alloy metal films. Residual AlCl3 left on the side walls of the patterned structure or on resist surfaces produces Al(OH)3 and HCl due to hydrolysis when exposed to water vapor, from air for example. This leads to corrosion of Al and Al alloy metal lines because Al and Al alloys are easily etched by chlorine containing acids, such as HCl.
A variety of methods have been created to prevent this corrosion, but it is still there. From the industrial semiconductor manufacturing point of view, such methods are supposed to be robust, effective, productive and inexpensive. Glow discharge plasma induction of oxygen, or its mixtures with nitrogen or noble gasses, are not effective.
U.S. Pat. No. 5,200,031 to Latchford et al. describes an in-situ stripping process for removing photoresist from an integrated circuit structure including the use of NH3. The Latchford et al. process can eliminate the concentration of corrosion responsible compounds, but can not prevent the corrosion.
U.S. Pat. No. 5,792,672 to Chan et al. describes an in-situ stripping process for removing a photoresist mask from an etched aluminum pattern including the use of H2O. However the Chan et al. process likewise can eliminate concentration of by-products that lead to corrosion, but can not prevent the corrosion.
A fluorine containing plasma stripping gas mixture, i.e. O2+CF4, may be used, but it will attack any open silicon oxide areas leading to over-etch of the underlying dielectric.
U.S. Pat. No. 5,462,892 to Gabriel discloses a method of anticorrosion processing a semiconductor wafer to inhibit corrosion of aluminum or other metal interconnection lines. The Gabriel method heats the wafers post etch up to 450xc2x0 C. to enhance desorbtion of AlCl3 from the wafer surface. However heating the wafers up to 450xc2x0 C. could cause changes in the mechanical and electrical features of the metal layout due to the recrystallization of the films that leads to a decrease in general reliability.
U.S. Pat. No. 5,578,166 to Hirota describes a copper or copper alloy reactive ion-etch (RIE) using a plasma of a gas mixture comprising a silicon tetrachloride (SiCl4) gas, a nitrogen (N2) gas, and a carbon compound gas that may typically be a carbon tetra-chloride (CCl4), methane (CH4), ethane (C2H6) and so on. Hirota does not deal with aluminum etch.
U.S. Pat. No. 5,350,484 to Gardner et al. describes a method for anisotropically etching metal interconnects especially in the fabrication of ULSI, high aspect ratio interconnects. Ions are implanted into a region of the metal film to be etched, to form a converted layer of metal compounds in the region. The converted layer is then selectively etched and removed at low temperatures with an etchant (HCl, NH4OH, MeOH, ether, alcohol, acetone and water for a copper metal film) chosen to decrease etching of the metal film. Gardner et al. deals with wet processes which are not taken into account.
U.S. Pat. No. 5,683,857 to Shirai et al. describes a method of forming a resist coat in a dry developing treatment and stripping the resist coat using an organic vapor. Shirai et al. deals with mask development, not etching.
U.S. Pat. No. 5,865,900 to Lee et al. describes a method for removing a metal-fluoropolymer residue from an integrated circuit structure within an integrated circuit employing an aqueous acid solution followed by an organic solvent. Lee et al. is a conventional technique which follows after metal etch and dry resist strip.
Accordingly, it is an object of the present invention to eliminate corrosion of aluminum or aluminum alloys metal films created on the surface of semiconductor wafers using etching in chlorine containing plasma.
Another object of the present invention is to remove or minimize/eliminate the deleterious effects of AlCl3 molecules in chlorine based plasma etching of aluminum or aluminum alloy metal films.
Other objects will appear hereinafter.
It has now been discovered that the above and other objects of the present invention may be accomplished in the following manner. Specifically, the remaining photoresist over an Al or Al alloy structure is removed after etching the Al or Al alloy structure in a chlorine based plasma. The Al or Al alloy structure being over a substrate. The Al or Al alloy structure, and the substrate are treated in-situ with organic solvent vapors (such as acetone or carbon tetrachloride) in the absence of plasma excitation at a first predetermined temperature and pressure. The remaining photoresist is then removed with a plasma activated oxygen flow at a second predetermined temperature and pressure.